Plasmids and Restriction Enzyme Mapping

Plasmids

• Circular, non-chromosomal pieces of DNA that can replicate in bacteria

• Often carry genes encoding resistance to antibiotics (like pGLO did for ampicillin)

• Are cut with restriction enzymes and then can be joined to a piece of DNA from any organism (foreign DNA) that has been cut with the same enzyme

Plasmids

• Can be mapped or described in terms of location of restriction sites using simple experiments and logic

• Sizes of the resulting DNA fragments are determined and then once can use logic to determine the relative location of the restriction sites

• Since plasmids are circular, the number of fragments represents the number of cuts or restriction sites (rubber band)

1000 bp plasmid exampleUndigested Digested with

Enzyme 1Digested with Enzyme 2

Digested with Enzyme 1 & 2

1000 bp700 bp

300 bp

1000 bp

500 bp300 bp200 bp

1000700

3001000

300

200

500

Extension Activity 1: Plasmid Mapping

• Plasmids and Restriction Enzymes– Read on own

• Reading a Plasmid Map Questions– P. 50-51 1-8 we will do together as a class– P. 52-54 1-12 you will work on in your lab groups– P. 58-59 1-4 and 1-4 new pages that you will work

on in your lab groups on Friday and turn in whole packet by end of the hour on Friday

1. From the map of plasmid S2 list all the restriction enzymes that

would cut the plasmid• Pvull• EcoR1• BamHI• Pstl• HindIII• Scal

2. Which plasmid, S2 or S5, is the biggest and what is its size?

• S5 is the largest• 9481 bp

3. Using plasmid S2 as an example, find the restriction sites for the enzyme Pvull. How many sites are there? What is their location? If Pvull was used to cut (digest)

this plasmid, how many fragments would it make?

• There are 3 sites for Pvull on plasmid S2

• They are at position 55, 1993, and 3410

• Three fragments would be created if plasmid S2 was digested with Pvull

4. Next determine the size of the fragments created when S2 is cut by Pvull. Size is

calculated by subtracting the site locations from each other. How big are the fragments from plasmid S2 that is cut with Pvull? The fragment sizes should add up to the total for that plasmid

(5869) base pairs

• The fragment sizes are 1417, 1938, and 2514 bp (5869 – 3410 + 55)

5. If the fragments from the plasmid S2 digested with Pvull were run on an agarose gel, what would they look like? Draw

the gel and label the fragments and their sizes

____ 2514

____ 1938

____ 1417

6. Now you can determine the fragment sizes of the plasmids when cut with the two enzymes. EcoR1 and Pstl. Indicate the sizes of the fragments that would be

generate if the plasmid were a digest by Pstl alone, EcoR1 alone or by both Pstl and EcoR1.

Enzyme EcoR1

Fragments 5869

Total 5869

Enzymes Pstl

Fragments 2860(5869-3307 + 298)1700 (1998-298)1159 (3307-2148)150 (2148-1998)

Total 5869Enzymes Both EcoR1 & Pstl

Fragments 2817 (5869-3307 + 255)1700 (1998-298)1159 (3307-2148)150 (2148-1998)43 (298-255)

Total 5869

7. If Plasmid S2 was digested and run on an agarose gel, what would the gel look like? Draw a gel and the fragment sizes if digested by EcoR1 alone,

Pstl alone, and by EcoR1 and Pstl together.

5869

8. How does your diagram in question #7 compare to what was observed in your gel after the experiment? Indicate a reason to why your data in

question #7 might be different from the actual experimental data seen from lesson 2.

• They should be similar but the bands at 150 and 43 are too small to be observed on the gel

Mapping the Plasmid Questions#1 How big is plasmid S5? Add the fragments in each

column. The total should add up to the size of the plasmid. Why?

• The plasmid is 9481 bp in size.

• The fragments are cut from the plasmid and all the pieces together should be equal to the size of the original plasmid.

2. Look at the data from the EcoR1 digest of plasmid S5. How many fragments are there? Did the enzyme cut the plasmid, or

did it remain as a circle? How could you tell?

• There should only be 1 fragment

• A first glance, it is not possible to tell if the plasmid was cut although sometimes a circular plasmid does not run through an agarose gel at the same place as a linear piece of DNA of the same size

#3 compare the data from the Pstl digest of plasmid S5 with that of the EcoR1 digest. How many fragments

are there? How many restriction sites are there for Pstl?

• There should be 7 fragments and therefore 7 restriction sites

#4 How many fragments are there when EcoR1 and Pstl are used to digest plasmid S5? Does that answer the question of

whether or not EcoR1 cut the plasmid? Why?

• There should be 8 fragments when the plasmid is cut by both enzymes.

• The additional fragment of Pstl digested plasmid S5 was shortened by an EcoR1 cut?

#5 Which fragment of Pstl digested plasmid S5 was shortened by an EcoR1

cut?• The 2860 bp

fragment was cut into 2 fragments (2817 bp and 43 bp)

#6 Draw the Pstl fragment that is cut with EcoR1 in plasmid S5 to demonstrate how the fragment was cut with EcoR1.

#7Restriction mapping is an exercise in critical thinking and logic. Plasmid S5 is difficult to

completely map because of the numerous Pstl restriction sites. With the data, it would be very difficult to place all the restriction sites in order. It is easier to map plasmid S3. How many times

did EcoR1 cut plasmid S3? What are the fragment sizes?

• EcoR1 cut plasmid S3 twice.

• The fragments are 863 and 6505 bp in size

#8 The data from the EcoR1 digest of plasmid S3 indicate that the fragments are not equal. Draw a

possible map and label the EcoR1 sites and the sizes of the fragments.

#9. Now draw an approximate map of the Pstl sites on plasmid S3 and label the Pstl sites and the sizes of the fragments.

#10. Draw a circular map of plasmid S3 digested with both Pstl and EcoR1? Mark sizes of each fragment and name the

restriction sites on your figure.

#11. Is there another possible order of restriction sites on plasmid S3 digested with both Pstl and EcoR1? How might you

resolve these possibilities?• Using the data from the

double digest there are 2 possibilities. However the single digest with Pstl would have fragments of 3687 and 3637 bp (not 4507 and 2860 as was seen).

#12 When the gels were run for this experiment, there were only 3 bands for plasmid S3. Which band is

missing from your gel? Why?• The 43 bp band is so

small that it does not bind enough stain to be visible or it may have run off the gel

Extension Activity 2: Constructing a Plasmid Questions

#1. Where is the Pstl site on the pTZ18U plasmid?

• Position 298

#2 Look at plasmid S4. What segment of the lambda bacteriophage has been inserted?

• Lambda fragment 5,218-9,617 was added

#3 After looking at the plasmid map and also the lambda phage map, can you determine how many Pstl restriction sites

were added to the plasmid because of the inserted lambda phage DNA fragment?

• Two restriction sites for Pstl were added: site 766 and site 3,604

#4 Look at plasmid S1. What segment of lambda was added to that plasmid? Were any Pstl restriction sites added to the

plasmid with the inserted fragment of lambda DNA?

• Lambda fragment 20,285 – 22,425 was added to plasmid S1. No additional Pstl sites were added.